From way back in 2008:
[November 03, 2008] "Sense/Net Adopts the CMIS Standard — the First in .NET World." By Tamás Bíró. Sense/Net 6.0 DevBlog. "We have developed a CMIS draft implementation in Sense/Net 6.0 Beta 2, soon to be released.
It is possibly the first .NET implementation, as all supporting companies except from Microsoft are JAVA based. It is surely the first open source implementation on the .Net platform... Since Sense/Net 6.0 is both an Enterprise Portal and an Enterprise Content
Management System, with its own Content Repository, we wanted to showcase how easy it is to use the .NET platform, WCF and Sense/Net 6.0 to implement the standard [see screenshot]. Our demo is a two way implementation, because our content repository has a
CMIS service interface and our portal has a CMIS client Webpart (portlet). So other CMIS clients can access our contents, but our portal can aggregate content from other CMIS compliant systems, such as next generation SharePoint, Alfresco and others. We are
also building an online CMIS demo, which is accessible from our website, but is under construction, so it might not work all the time. [Simple CMIS Client, Simple CMIS Aggregate Client] The demo features two CMIS webparts. One is able to navigate the content
repository; the other is able to aggregate content from two sources that you can enter. The screenshot above is the CMIS test webpart, showing the PFS root contents. The services can also be accessed, just copy the URI-s from the input boxes. It even works
with a simple browser, showing XML. There is no authentication, so no login is required. The source code will be available within a few days..." Related information from the Sense/Net Wiki: "How Does the Implementation of CMIS Work with Sense/Net
6.0?" [See also Sense/Net Enterprise Portal and ECMS from CodePlex, and "Sense/Net Pledges Support for CMIS Standard" from CMS Critic.]
http://sensenet.codeplex.com/ has a .net CMIS implmentation in it's open source download.
I've not had a chance to look at it yet, but will report back when I have